My first posting. Just lost my gear in the Queensland floods.
Have now purchased a Canon 40D, and am considering Sigma or Canon lens for photographing birds.
I'd more or less settled on Canon100-400IS, when I saw the Sigma 50-500 OS advertised.
I'll search for any previous postings on these two lenses, (but I can't do that till I've made my first posting).
Any or all ideas welcome!